Despite an increased bacterial burden, infection with wild-type S. pyogenes actually reduced CXCL1/KC levels in muscle tissue (median, 37 ng ml−1; range, 23–49 ng ml−1) compared with mice infected with the cepA mutant (median, 78 ng ml−1; range, 37–93 ng ml−1; P < 0.001), consistent with chemokine inactivation by SpyCEP (Fig. 3), since the enzyme-linked immunosorbant assay (ELISA) recognizes only full-length rather than cleaved CXCL1/KC. This evidence concerns the gene CXCL1 and infection.